Recoil devices dissipate the energy of gunfire at a controlled rate so as to minimize the recoil force transferred to the gun carriage without exceeding the available length of recoil. In a simple hydraulic recoil device the recoiling mass is given an initial velocity by the firing impulse. The recoiling mass drives a piston in a hydraulic cylinder against the hydraulic fluid causing the fluid to flow out of the cylinder through an orifice area, as shown in FIG. 1. The orifice ,area is a function of the position of the recoiling mass and the functional relationship is chosen to transfer the desired force as a function of time to the carriage.
The desired force/time relationship is usually trapezoidal in shape, as shown by the dashed line in FIG. 2, wherein the force rises rapidly to a maximum and maintains this maximum through the recoil cycle, and then drops quickly to a lower pressure which is maintained through the counter-recoil cycle. The pressure in the hydraulic cylinder follows the same time response as this force. As shown by the trapezoidal force/time curve, the peak force transmitted to the carriage is minimum when the recoil force is constant over the available recoil distance, and is the usual objective of the recoil mechanism designer. However, military howitzers fire a variety of projectiles using a number of different propellant charges (zone charges). Therefore the recoil mechanism must function satisfactorily for a wide range of firing impulses and elevation angles.
The conventional recoil mechanism thus described is an open loop control system, wherein the pressure in the hydraulic cylinder is controlled by an orifice which is designed using a priori knowledge of the system response. However, the problems associated with this open loop control system are common to any open loop controller in that the system does not account for variation in the input (impulse), operating conditions (elevation angle), environment (ambient temperature) and plant (result of many firings), and the system performance is degraded.
Modern recoil mechanisms are designed to attain the desired pressure or force characteristics under the most severe conditions, namely maximum impulse. However, variations in input result from the use of both lower impulse rounds (lighter rounds or lower zone charges) and higher impulse rounds, the latter being often introduced after a system is fielded. Also, while systems have been designed that will achieve the desired response for two recoil lengths, one for low elevation angles (long recoil) and one for high elevation angles (short recoil), the peak force is of course larger in the case of the short recoil.
Accordingly, it would be desirable to provide a control system which can adapt to different firing charges. S. M. Wu and A. N. Madiwale have proposed a mathematical model for a modified hydropneumatic recoil mechanism, wherein a separate control law is designed for each firing charge and the control law corresponding to the charge being fired is selected from this predesigned set. This control scheme can be implemented by the addition of servo valves operating in tandem with the variable area orifice of a conventional recoil mechanism in which the feedback gains for the servo valve can be selected from a predesigned set by identifying the charge being fired by sensing signals such as acceleration with the help of a microprocessor (Technical Report No. R-TR-77-024, "Optimal Control of Active Recoil Mechanism", February 1977, Prepared for Engineering Directorate & General Thomas J. Rodman Laboratory, Rock Island Arsenal, Rock Island, Ill.). See also Proceedings of 2nd Annual U.S. Army Symposium on Gun Dynamics, Publication ARLCB-SP-78013,19-22 September 1978, and also ASME Publication 78-WA/DSC-12, December 1978, "Optimal Adaptive Control of Active Recoil Mechanisms", A. N. Madiwale, R. E. Kasten, S. M. Wu and R. J. Radkiewicz.